1. Field of the Invention
This invention relates to coating techniques, and is particularly directed to an improved method and apparatus for annealing thin-film coatings.
2. Description of the Prior Art
The concept of coating a substrate with a layer of a different material has long been known as a technique for protecting the substrate from deleterious conditions or for improving the appearance, performance, or cost of the resulting article. Thus, for example, it has been found that articles can be formed rapidly and cheaply out of plastic, and can be coated to simulate metal articles which would be much more expensive. Alternatively, articles can be formed of inexpensive, easily worked substrates and can be coated to provide improved thermal or electrical properties or other desired characteristics.
Unfortunately, many coating techniques require deposition of two or more materials to form the coating and, often, chemical interaction between the deposited materials is required in order to obtain the desired results. In view of this, considerable care and accuracy must be given to assure that the proper proportions of the respective ingredients are achieved and, frequently, special treatment of the deposited materials is needed to cause desired combining of the deposited materials to form the desired coating.
One major problem of such coating techniques is that of preventing contaminant materials from becoming deposited on the substrate to reduce or destroy the effectiveness of the resulting coating. To overcome this problem, deposition processes are frequently carried out in vacuum chambers, and many methods and apparatus for performing vacuum deposition have been proposed. However, with all of the prior-art vacuum deposition techniques, it has been difficult or impossible to monitor the deposition process while it was being carried out. Therefore, where precision coating is required, it has been necessary to perform the vacuum deposition process in a series of steps interspersed with inspection periods. Obviously, this procedure requires repeated charging and discharging of the vacuum chamber, which is expensive and time-consuming and may, in itself, cause defects in the coating. As a result, the general practice of the prior art has been to ignore monitoring of the deposition process and to rely, instead, upon monitoring the rate of discharge of the materials to be deposited from their respective sources. However, this is an indirect indication of deposition, at best, and provides no means for detecting or eliminating contaminant materials.
Another problem of prior art vacuum deposition techniques arises when it is necessary or desirable to apply heat to enhance attachment of the deposited materials to the substrate, to promote chemical interaction of the deposited materials with other deposited materials or with the substrate, or to anneal the coating materials and to drive off contaminant materials. Unfortunately, such heat treatment frequently requires the use of high temperatures which may be above the melting point of many potential substrate materials, while many other materials may crack or become warped when exposed to such high temperatures. Thus, may candidate substrate materials must be eliminated when such heat treatment is required.